3 Layout
In this section we present an overview of the changes which are considered in the ILC layout. While
some of these changes are consequences of the proposed changes in the subsystem designs and are
integral part of the SB2009 proposal, some have come about through continuing system design and
development prior to the SB2009 re-baseline studies.
Figure 3.1 shows schematic layouts of the ILC as proposed in the Reference Design Report (RDR), and
as foreseen today in the SB2009 proposed new baseline.
Figure 3.1: Schematic layouts of the ILC as proposed in the Reference Design Report (RDR) on the
left, and as foreseen today in the SB2009 proposed new baseline on the right.
The most obvious changes are in the central region, or specifically, the Damping Rings (DRs). Shortly
after the publication of the RDR, the circumference of the DR’s was changed from 6.7 to 6.4 km to
correct a inconsistency between the orbital revolution frequency of the rings and the RF frequencies
of the injector buncher systems. This 6.4 km, six-fold symmetric ring design was located around the
interaction region and elevated by 10 m above the Beam Delivery systems along with the e- injector
and e+ KAS, (keep alive source). This allowed some independence in operation of the injectors and
rings from personnel access to the Beam Delivery Systems (BDS).
When considering the detail component layout of the six-fold ring, which has to accommodate RF
systems, wigglers, circumference chicanes and injection and extraction systems, a different
philosophy was explored. It is a two-fold design ‘race track geometry’ with long straight sections
which included the same systems as in the previous design. The lattice of the arc sections was
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changed to a new very flexible one, where the emittance and momentum compaction could be
separately adjusted. These changes were accepted in 2008 before the SB2009 formal process was
begun. For further detail regarding DR component layouts, see Section 4.5.
These changes in geometry stimulated discussions regarding alternate layouts of the central region.
Of particular interest are the changes made possible with the race track design, where the beam
injection and extraction occur at nearly the same point in the center locations of one of the two long
straight sections. Therefore, one can consider a DR to offset horizontally from the BDS and
Interaction Region, but in the same plane, with short beam transfer lines between them. This, then,
led to discussions of a compact and efficient central region, which incorporated all of the E+/injection systems, DR’s, BDS and Interaction Region in a single central campus. The long linac tunnels
containing both the main linac and RTML beamlines would then extend outwards in either direction
without interruptions. Here, the use of the word efficient refers to minimizing the necessary
underground volume of tunnels, caverns and shafts.
These ideas were combined with the construction scheme of the main linacs on the basis of the
single-tunnel scheme, the Low Power option and Single Stage Bunch Compression into the AD&I
Studies and the SB2009 Design.
The single-tunnel linac layout incorporates the proposed single-stage bunch compressor. This singlestage bunch compressor ends up with the beams at ~ 5GeV as opposed to 15 GeV in the two-stage
design. However, the changes of the geometry (distance along the beam line) to reach 15 GeV is
minimall. The major change is that in the E- linac the total E+ generating system is moved to the
central region, and therefore, the E- and E+ linacs are now identical, except for a short extra linac
hardware to compensate for the beam energy loss incurred by the use of undulator to produce
photons for positron generation. (the 2009 e+ conservative design has ~ 1.5 GeV more loss than the
RDR). This means that changes in accelerating gradient, gradient distribution or maximum design
energy, are easily accommodated. Changes of gradient of the order of 10% would not require little in
the way of fundamental changes in the layout or of infrastructure support from CF&S.
The central region is more complex and more difficult to describe. It is also difficult to display
schematically unless a large artificial ratio is used between the longitudinal and transverse scales.
Figure 3.2 shows the concept of beam lines which share tunnels in this region and these are included
in the real tunnel schematics which can be found
at ILC layout diagrams at
http://ilc.kek.jp/SB2009/TUNNEL%20DRAWING%20SET%20(11-20-2009).pdf .
Figure 3.2: Topological diagram of the beamlines in the ILC central area.
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Many of the design details and changes of these systems are described in Section 4. The following is
a discussion of the general layout and the design philosophy.
The goal was to minimize the underground volume, as stated above, while developing the individual
system designs and interfaces with CF&S beyond where they were at the time of the RDR. As the
injectors and beam delivery systems which share beam line tunnels, are very varied in there support
requirements (power supplies, RF, instrumentation etc), it was decided at an early stage of the
studies that there would continue to be a single support tunnel for the central region. This is unlike
the linac where each of the ~10+ km linac is comprised of repetitive units each extending over ~30 m.
Even in the presence of this support tunnel, there is a reduction of ~5 km out of ~14 km in tunnel
length in central region, not including the DR’s.
The “Low Power” option, with half the number of bunches, enables, but does not require, a half
circumference damping ring. This layout accommodates either of 3.2 or 6.4 km rings. It is because
the 1 km straight section, which includes the injection and extraction from both rings, does not
change in location or geometry with a change in circumference. The larger ring would have arcs with
an increased radius, and again, an almost identical straight section for the RF and wigglers.
Much of the effort to date has been on the region where the E+ production systems and the beam
delivery systems co-exist. In the RDR, the E+ production system had to co-exist with the 150 GeV Ebeam which after the E+ system continued on to the IR. There were conceptual designs at the time of
the RDR, whereas today, the designs now address many more practical engineering issues. For
example, there are short sections of tunnel which will need “alcoves”. The alcoves will require to
implement locally different tunnel cross-sections which are dependant on the local geology. Many of
these issues were duplicated in the “Keep alive source” (KAS) in the RDR. The KAS has now been
replaced by an “Auxiliary Source”, where an E- beam uses the same target, capture, booster systems
as the gamma beam from the undulator. In the SB2009 design, now, there is only one vault which is
designated to handle high radiation environment. (still to be determined but see below on MPS)
The transition from a linac with a wide acceptance in energy and transverse phase space, to a small
acceptance undulator or to a tight BDS requires both protection collimation and abort systems. In
SB2009 a single section of collimation and abort system will protect both the undulator and the BDS
in an integrated fashion, since the undulator is located at the end of the linac leading into the BDS.
This is expected to offer an improvement in day to day operation which is difficult to quantify
The E- injector easily fits into the SB2009 layout, whose geometry choice is primarily determined by
the requirements from the E+ injector side. A natural asymmetry in the length of E- and E+ sides is
exploited to incorporate a E+/- timing delay drift length which is expected to amount to a few
hundred meters. It is highly desirable as stated in the RDR, that one injects into (fills) an empty DR
bucket which has just been empted by extraction. This puts constraints on the difference in path
lengths travelled by the electrons and positrons through the RTMLs, linacs and BDS’s and the DR
circumference. At the time of the RDR, while this issue was well known, a fully worked-out beamline
implementation solution was not presented, because with that layout and 6.4 km DR’s the path
length correction had to be kilometers. In the SB2009 layout and with the 3.2 km rings, this
correction can now be a few hundred meters.
There are other examples where the SB2009 designs and layouts are more complete and detailed
than the RDR. This is due to both the continuing design work over the time since the RDR but also
driven by the AD&I studies of the SB2009 proposal. In some places this complicates comparisons.
The detail system designs and their pro’s and con’s are based on these layouts and are discussed in
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detail in the following sections. Figure 3.3 shows the overall schematic machine layout and Figure
3.45 gives the schematic directional beamline layout.
Figure 3.3: Overall Schematic Machine Layout
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Figure 3.4: Schematic Directional Beamline Layout
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